U.S. patent number 6,929,851 [Application Number 09/627,801] was granted by the patent office on 2005-08-16 for coated substrate.
This patent grant is currently assigned to TDY Industries, Inc.. Invention is credited to John Bost, Roy V. Leverenz.
United States Patent |
6,929,851 |
Leverenz , et al. |
August 16, 2005 |
**Please see images for:
( Certificate of Correction ) ** |
Coated substrate
Abstract
Method for removing a portion of the binder phase from the
surface of a substrate that is composed of particles of at least a
first phase joined together by the binder phase, and wherein the
surface is etched by contacting it with a gas flow of an etchant
gas and a second gas. The second gas is one or more gases that will
not react with the substrate or the removed binder phase and will
not alter the oxidation state of the substrate during etching.
Inventors: |
Leverenz; Roy V. (Smyrna,
TN), Bost; John (Franklin, TN) |
Assignee: |
TDY Industries, Inc.
(Pittsburgh, PA)
|
Family
ID: |
22251805 |
Appl.
No.: |
09/627,801 |
Filed: |
July 28, 2000 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
095398 |
Jun 10, 1998 |
6214247 |
|
|
|
Current U.S.
Class: |
428/216; 428/336;
428/469; 428/472; 428/697; 428/698; 428/699; 51/307; 51/309 |
Current CPC
Class: |
C23C
16/0236 (20130101); C23C 16/34 (20130101); C23C
16/36 (20130101); C23C 30/005 (20130101); Y10T
428/265 (20150115); Y10T 428/24975 (20150115) |
Current International
Class: |
C23C
16/02 (20060101); C23C 30/00 (20060101); C23C
16/36 (20060101); C23C 16/34 (20060101); B32B
009/00 () |
Field of
Search: |
;428/698,472,469,336,697,699,408,701,216,702 ;51/307,309 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Turner; Archene
Attorney, Agent or Firm: Kirkpatrick & Lockhart
Nicholson Graham LLP
Parent Case Text
This is a divisional application of U.S. Ser. No. 09/095,398, filed
Jun. 10, 1998, now U.S. Pat. No. 6,214,247.
Claims
We claim:
1. An article, comprising a composite portion comprising hard
constituent particles in a binder; an etched surface region
substantially free of eta phase, the etched surface region
comprising substantially intact hard constituent particles and
voids between the substantially intact hard constituent particles,
wherein the voids extend to the composite portion and to a depth of
between about 3 microns and about 15 microns; and a wear resistant
coating on the etched surface region and disposed in the voids.
2. The article of claim 1, wherein the composite portion comprises
at least one of cemented carbides and cermets.
3. The article of claim 1, wherein the hard constituent particles
comprise one or more material selected from the group consisting
of: a carbide material selected from the group consisting of
tungsten carbide, titanium carbide, tantalum carbide, niobium
carbide, vanadium carbide, chromium carbide, molybdenum carbide,
and iron carbide; a carbonitride of a refractory metal; a nitride
of a refractory metal; a carbonitride of an element selected from
the group consisting of W, Ti, Ta, Nb, V, Cr, Mo, and Fe; an oxide
of an element selected from the group consisting of aluminum,
zirconium, and magnesium; a boride of an element selected from the
group consisting of aluminum, zirconium, and magnesium; a material
comprising molybdenum; and a material comprising tungsten.
4. The article of claim 1, wherein the hard constituent particles
comprise tungsten carbide and the binder comprises cobalt.
5. The article of claim 1, wherein the binder comprises one or more
materials selected from the group consisting of cobalt, nickel,
iron, elements within Group VIII of the periodic table, copper,
tungsten, zinc, and rhenium.
6. The article of claim 1, wherein the coating enhances the wear
resistance of the article and is comprised of one or more materials
selected from the group consisting of TiC, TiN, TiCN, Al.sub.2
O.sub.3, TiAlN, HfN, HfCN, HfC, ZrN, ZrC, ZrCN, Cr.sub.3 C.sub.2,
CrN, and CrCN.
7. The article of claim 1, wherein the coating is an MT-milling
coating.
8. The article of claim 1, wherein the article is selected from the
group consisting of metal cutting inserts, dies, punches, stamps,
threading devices, blanking devices, milling devices, turning
devices, drilling devices, boring devices, mining bits, drilling
bits, tricone bits, percussive bits, road planing devices, wood
working bits, wood working blades, drawing devices, heading
devices, back extrusion devices, rod mill roll devices, and wear
parts used in corrosive environments; and the coating enhances the
wear resistance of the article.
9. An article, comprising: a composite portion comprising hard
constituent particles in a binder; an etched surface region
substantially free of eta phase, the etched surface region
comprising substantially intact hard constituent particles and
voids between the substantially intact hard constituent particles,
wherein the voids extend to the composite portion to a depth of
between about 3 microns and about 15 microns; and a wear resistant
multi-layer insert coating on the etched surface region and
disposed in the voids, wherein the wear resistant multi-layer
insert coating comprises two TiN layers of approximately 1 micron
with a TiCN layer of approximately 3 microns disposed between the
two TiN layers.
10. The article of claim 9, wherein the composite portion comprises
at least one of cemented carbides and cermets.
11. The article of claim 9, wherein the hard constituent particles
comprise one or more material selected from the group consisting
of: a carbide material selected from the group consisting of
tungsten carbide, titanium carbide, tantalum carbide, niobium
carbide, vanadium carbide, chromium carbide, molybdenum carbide,
and iron carbide; a carbonitride of a refractory metal; a nitride
of a refractory metal; a carbonitride of an element selected from
the group consisting of W, Ti, Ta, Nb, V, Cr, Mo, and Fe; an oxide
of an element selected from the group consisting of aluminum,
zirconium, and magnesium; a boride of an element selected from the
group consisting of aluminum, zirconium, and magnesium; a material
comprising molybdenum; and a material comprising tungsten.
12. The article of claim 9, wherein the hard constituent particles
comprise tungsten carbide and the binder comprises cobalt.
13. The article of claim 9, wherein the binder comprises one or
more materials selected from the group consisting of cobalt,
nickel, iron, elements within Group VIII of the periodic table,
copper, tungsten, zinc, and rhenium.
14. The article of claim 9, wherein the article is selected from
the group consisting of metal cutting inserts, dies, punches,
stamps, threading devices, blanking devices, milling devices,
turning devices, drilling devices, boring devices, mining devices,
drilling bits, tricone bits, percussive bits, road planing devices,
wood working bits, wood working blades, drawing devices, heading
devices, back extrusion devices, rod mill roll devices, and wear
parts used in corrosive environments; and the coating enhances the
wear resistance of the article.
Description
TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION
The present invention relates to a method for etching composite
material substrates and other substrates, and also is directed to a
method for applying wear-resistant and other coatings to composite
material substrates and other substrates. The present invention
also relates to composite material substrates, which are comprised
of particles of a hard constituent phase in a binder material phase
that binds together the hard constituent particles, having
wear-resistant and other coatings. The present invention finds
application in any field in which it is advantageous to enhance the
adhesion of a wear-resistant and other types of coatings to
substrates. Examples of fields of application of the present
invention include the manufacture and treatment of dies used in
metal stamping, punching, threading, and blanking, and the
manufacture and treatment of metal cutting inserts used in milling,
turning, drilling, boring, and other metal removal operations.
BACKGROUND OF THE INVENTION
Composite materials comprised of particles of a hard constituent
phase and a binder phase binding the particles together are common
and are referred to as composite materials or "composite
substrates" hereinafter. Such materials also may be referred to as
"cemented" composite materials and include, for example, ceramics,
cermets, and cemented carbides. Cemented carbides, include, for
example, materials composed of a hard particulate material such as,
for example, particles of one or more of tungsten carbide (WC),
titanium carbide (TiC), titanium carbonitride (TiCN), tantalum
carbide (TaC), tantalum nitride (TaN), niobium carbide (NbC),
niobium nitride (NbN), zirconium carbide (ZrC), zirconium nitride
(ZrN), hafnium carbide (HfC), and hafnium nitride (HfN) cemented
together by a binder phase that is composed predominantly of one or
more of cobalt, nickel, and iron.
Metal cutting inserts fabricated from composite materials are
commonly used in chip cutting machining of metals in the metal
machining industry. Metal cutting inserts are commonly fabricated
from particles of metal carbide, usually tungsten carbide with the
addition of carbides of other metals such as, for example, niobium,
titanium, tantalum, and a metallic binder phase of cobalt or
nickel. The carbide materials provide high strength but still may
wear quickly when used in, for example, milling and other metal
machining operations. By depositing a thin layer of wear-resistant
material on the working surfaces of cemented carbide cutting
inserts it is possible to increase the wear-resistance of the
inserts without adversely affecting toughness. Commonly used
wear-resistant cemented carbide insert coatings include, for
example, TiC, TiN, TiCN, and Al.sub.2 O.sub.3. Such wear-resistant
coatings reduce the erosion and corrosion of the inserts' binder
material.
The utility of coated composite materials such as coated cemented
carbides is limited by the strength of adhesion of the
wear-resistant coating to the composite material. Absence of strong
adhesion between wear-resistant coatings and metal cutting inserts
causes delamination of the coatings from the inserts, decreasing
the inserts' service life. The presence of cobalt at the inserts'
surfaces also increases the tendency of the coatings and substrates
to experience delamination during use. Accordingly, it would be
advantageous to provide a novel method for increasing the adhesion
of wear-resistant coatings to composite materials. More broadly, it
would be advantageous to enhance the adhesion of wear-resistant
coatings and other types of coatings to composite material and
other types of substrates.
SUMMARY OF THE INVENTION
The present invention provides a method for removing a portion of
the binder phase from a substrate that is composed of at least
particles of a first phase joined together by the binder phase. The
present method includes the step of etching at least a portion of a
surface of the substrate by contacting the surface with a gas flow
that is composed of at least an etchant gas and a second gas for a
time period that will allow for removal of the desired amount of
binder phase. The second gas comprises one or more gases that will
not react with the substrate or the removed binder material and
that will not alter the oxidation state of the substrate during the
etching step. Preferably, the second gas is one or more gases that
will not react with the substrate or the removed portion of binder
material to form deposits of a phase of W.sub.x CO.sub.y C (wherein
x=3-9 and y=2-6), also referred to herein as an .eta. (eta) phase,
on the substrate.
The etchant gas used in the present method may be any gas or
combination of gases that will suitable remove the desired portion
of the binder phase from the substrate during the etching step.
Possible etchant gases include hydrogen chloride gas, H.sub.2
F.sub.2 gas, and gaseous forms of any of the Group VIIA elements.
Other possible etchant gases useful in the present method will be
apparent to those having ordinary skill once apprised of the
present invention. The second gas may be, for example, one or more
gases selected from nitrogen gas, helium gas, argon gas, and neon
gas. Preferably the gas flow is applied to the substrate during the
etching step by introducing a flow of the etchant gas concurrently
with a flow of the second gas into a chamber containing the
substrate at a pressure and temperature, and for a time, that will
result in removal of the desired portion of the binder phase. In
one particular application of the present method, the gas flow
consists of concurrent flows of hydrogen chloride gas and nitrogen
gas.
Preferably, during the etching step binder phase is removed from a
surface of the substrate to a depth of between about 3 microns to
about 15 microns, and more preferably to a depth of between about 4
microns to about 6 microns.
The method of the present invention preferably is applied to
substrates composed of a composite material comprising particles of
a hard constituent material joined together by a binder material.
Examples of such composite materials include cemented carbides and
cermets. Examples of the binder material of such composite
materials include materials composed of one or more materials
selected from cobalt, nickel, iron, elements within Group VIII of
the periodic table, copper, tungsten, zinc, and rhenium. Once
apprised of the details of the present invention, one of ordinary
skill in the substrate coating and treatment arts will comprehend
additional composite materials to which the present invention may
be applied.
The present invention also is directed to a method for applying a
coating to at least a portion of the surface of a substrate,
preferably a composite substrate that includes hard constituent
material particles joined together by a binder. The method is
carried out by removing a portion of the binder from a surface of
the substrate by contacting the surface with a gas flow including
an etchant gas and a second gas for a period of time that will
remove the desired portion of binder. The surface etching effect of
the etchant gas provides an etched surface on the substrate, and
the etched surface will include voids produced as the binder is
etched away from between hard constituent particles. The second gas
is one or more gases that will not react with the substrate or the
portion of the binder removed from the substrate, and that will not
change the oxidation state of the substrate during the etching
process. Preferably, the second gas will not react during the
etching process to form eta phase within the voids etched in the
substrate's surface. In a subsequent step of the method, a coating
is applied to at least a portion of the etched surface. At least a
portion of the coating is deposited within at least a portion of
voids on the etched surface created by removal.
Thus, the etching step of the present invention may be preceded or
followed by one or more additional steps, including, for example,
the step of depositing a coating on the etched surface of the
substrate produced by the etching step. Because the coating
infiltrates voids in the etched surface of the substrate that have
been produced by removal of binder material during the etching
step, the adhesion of the coating to the substrate is enhanced.
Preferably, the coating is one that enhances the wear resistance of
the substrate, but it also may be selected from any other
conventional substrate coating. Possible wear-resistant coatings
that may be applied in the coating step of the present method
include those composed of, for example, one or more of TiC, TiN,
TiCN, diamond, Al.sub.2 O.sub.3, MT-milling coating (described in
detail below), TiAlN, HfN, HfCN, HfC, ZrN, ZrC, ZrCN, BC, Ti.sub.2
B, MoS, Cr.sub.3 C.sub.2, CrN, CrCN, and CN.
The present invention is also directed to substrates that have been
produced by the method of the present invention. For example, such
substrates within the scope of the invention may have an etched
surface produced by the foregoing etching step, and also may have a
coating, wear-resistant or otherwise, which at least partially
infiltrates voids produced in the substrate's surface by the
etching step of the invention. In particular, the present invention
is directed to a substrate composed of a composite material
including particles of a hard constituent material and a binder
material. The substrate includes an etched surface portion having
voids thereon produced by removing a portion of the binder material
therefrom by contacting the surface portion with concurrent flows
of at least a suitable etchant gas and a second gas. The second gas
must be incapable of reacting with the substrate or the removed
binder material or changing the oxidation state of the substrate
during etching of the binder material. A coating may be adhered to
at least a portion of the etched surface portion of the substrate,
and at least a portion of the coating is deposited within at least
a portion of the voids provided in the etched surface portion.
Examples of applications of the method of the present invention
include the manufacture and treatment of wear resistant cutting
inserts, dies, punches, and other elements used in applications
such as: metal stamping, punching, threading, blanking, milling,
turning, drilling, boring, and other metal removal operations;
mining and oil drilling, including fabricating or treating mining
and drilling bits used in long wall and coal boring miners,
tricone, percussive and rooftop drilling bits, road planing and
other like applications; wood working applications, including
fabricating or treating bits and blades used in sawing, planing,
routing, shaping, and other woodworking applications; drawing,
heading, and back extrusion, including the fabrication and
treatment of punches and dies used in such applications; rod mill
rolls; and high corrosion environments. An example of a specific
application of the present invention is in the manufacture and
treatment of items made from tungsten-based alloys containing iron,
nickel, copper and/or cobalt. Such items include, for example,
aircraft weights, electrical contact points, and electrodes.
The reader will appreciate the foregoing details and advantages of
the present invention, as well as others, upon consideration of the
following detailed description of the invention. The reader also
may comprehend such additional details and advantages of the
present invention upon practicing the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The features and advantages of the present invention may be better
understood by reference to the accompanying figures, in which:
FIG. 1 is a photomicrograph of a prepared section of a metal
cutting insert composed of SD-5 material coated with wear-resistant
MT-milling (moderate temperature milling and turning) coating by
the method of the present invention;
FIGS. 2a-2c and 3a-3c are photomicrographs showing the condition of
an edge surface of each of three metal cutting inserts, composed of
SD-5 material and coated with an MT-milling coating by the method
of the invention, after 10 and 18 milling passes, respectively;
FIGS. 4a-4c and 5a-5c are photomicrographs showing the condition of
an edge surface of each of three uncoated metal cutting inserts,
composed of SD-5 material, after 10 and 18 milling passes,
respectively;
FIGS. 6a-6c are photomicrographs showing the condition of an edge
surface of three metal cutting inserts, composed of T-14 material
and coated with an MT-milling coating by the method of the
invention, after 4 milling passes;
FIGS. 7a-7c are photomicrographs showing the condition of an edge
surface of three metal cutting inserts composed of T-14 material,
each insert both unetched and uncoated, after 4 milling passes;
FIG. 8 is a photomicrograph of a metal cutting insert composed of
H-91 material and coated with an MT-milling coating by the method
of the present invention;
FIG. 9 is a photomicrograph showing the condition of a metal
cutting insert, composed of H-91 material and coated with an
MT-milling coating by the method of the invention, after one
milling pass;
FIG. 10 is a photomicrograph showing the condition of a metal
cutting insert, composed of H-91 material and coated with an
MT-milling coating of TiN/TiCN/TiN layers totaling approximately 5
microns (applied by CVD), after one milling pass; and
FIGS. 11a-11d are photomicrographs of a prepared section of a heavy
metal part containing tungsten metal particles (about 90 weight
percent of the part's total weight) suspended in an iron/nickel
binder (about 10 weight percent of the part's total weight) that
was etched and coated with an MT-milling coating by the method of
the present invention.
DETAILED DESCRIPTION OF THE INVENTION
An aspect of the present invention is directed to a method for
applying a coating, preferably a wear-resistant coating, to a
composite material substrate. The composite material substrate
includes a phase of a hard constituent and also includes a binder
phase that is predominantly one or more of cobalt, nickel, and
iron. The present inventors have discovered that the method of the
invention enhances the adherence of the coating to the composite
material substrate and inhibits delamination of the coating. The
present invention also is directed to etched and etched/coated
substrates prepared by the method of the present invention.
It is believed that in relation to the known composite material
substrate coating methods, the present method improves adhesion
between composite material substrates and wear-resistant coatings
by allowing the coatings to infiltrate the surface of the
substrate. To accomplish this, a portion of the binder phase of a
surface region of the composite material substrate is removed by a
novel etching procedure, preferably to a depth in the range of
about 3 to about 15 microns (inclusive), while leaving the hard
constituent particles in the surface region substantially intact.
Wear-resistant coatings applied to composite material substrates
that have been etched by the present method infiltrate the voids in
the surface region created by removal of the binder phase. The
infiltration of the coating is believed to increase the adhesive
strength between the coating and the composite material substrate.
It has been found that the enhanced adhesion between coatings and
composite material substrates achieved by the present method
reduces differences in thermal expansion between the substrates and
coatings, improves the coatings' resistance to deformation,
increases coating wear resistance, and reduces the occurrence of
thermal cracking.
As used herein, "composite material" refers to a material, in any
form, that includes at least particles of a phase of a hard
constituent material and a phase of a binder material that binds
together the hard constituent particles. The composite material may
be, for example, cemented carbides and cermets. The binder material
of the present composite material may include one or a combination
of more than one of cobalt, nickel, copper, and iron. In addition
to cobalt, nickel, copper, and/or iron, the binder material may
include other elements and compounds as are known in the art. Such
other elements include, for example, those within Group VIII of the
periodic table (elements having atomic numbers 26-28, 44-46, and
76-78), tungsten, zinc, and rhenium. The particles of the hard
constituent may be, for example, particles composed of:
one or more carbide materials selected from tungsten carbide (WC),
titanium carbide (TiC), tantalum carbide (TaC), niobium carbide
(NbC), vanadium carbide (VC), chromium carbide (Cr.sub.3 C.sub.2),
molybdenum carbide (MoC), and iron carbide (FeC);
one or more carbonitrides and/or nitrides of one or more of the
refractory metals, including carbonitrides of one or more of W, Ti,
Ta, Nb, V, Cr, Mo, and Fe;
one or more oxides and/or borides of one or more of aluminum,
zirconium, and magnesium; and
one or more of tungsten, molybdenum-based materials, and
tungsten-based materials.
As used herein, the term "refractory metals" refers to metals
having an extremely high melting point, for example, W, Mo, Ta, Nb,
Cr, V, Re, Ti, Pt, and Zr.
In addition to enhancing the adhesion of wear-resistant coatings to
the foregoing composite materials, it is believed that the method
of the present invention also may be used to enhance the adhesion
of wear-resistant and other types of coatings to other types of
materials, including, for example, heavy metals, sialons, Si.sub.3
N.sub.4, and composite ceramics, that have a phase that may be
etched by the present method. The identities of such other
materials may be readily determined by those having ordinary skill
in the substrate coating arts. Moreover, although the following
examples are directed to the application of wear-resistant coatings
to composite material and other substrates, it will be understood
that the present method also may be used to better adhere other
types of coatings to such substrates. Such other coatings include
coatings that impart desirable properties to the substrate surface,
such as, for example, coatings that enhance the substrate's
resistance to corrosion, including oxidation, or that provide a
particular surface appearance to the substrate. The identities of
other coatings that may be applied using the method of the present
invention will be readily apparent to those having ordinary skill
in the substrate coating arts once apprised of the invention.
In one embodiment of the method of the present invention, the
method generally includes at least the following steps:
1. Place a composite material substrate to be coated in a chamber
of a chemical vapor deposition furnace.
2. Etch away all or a portion of the binder phase in a surface
region of the composite material substrate to a depth of about 3
microns to about 15 microns by contacting the surface region with a
mixture comprising an etchant gas and an inert gas such as nitrogen
gas. (The etchant gas may be selected from, for example, gaseous
hydrogen chloride, gaseous H.sub.2 F.sub.2, or the gaseous form of
any of the Group VIIA elements. Other suitable etchant gases will
be apparent to those of ordinary skill in the art or may be
determined by such persons without undue experimentation, and it
will be understood that the identity of such suitable alternative
etchant gases will depend on the particular composition of the
material that is to be etched. The gaseous mixture is applied to
the surface of the material to be etched under conditions and for a
time suitable to remove the desired amount of binder phase from the
material. Such conditions and times may be readily ascertained,
without significant experimentation, by those having ordinary skill
in the substrate coating arts.)
3. Purge the chamber with a flow of an inert gas ("inert" meaning
that it will not react with the binder material) such as, for
example, nitrogen, argon, or helium gas.
4. Coat the etched region of the composite material substrate with
at least one layer of a wear-resistant material by introducing a
reactive gaseous form of the wear-resistant material into the
chamber under conditions that will result in the deposition of the
wear-resistant material on the etched region. (Such conditions,
which generally include such parameters as reactive gas flow rates,
chamber gas pressure, chamber and/or substrate temperature, and
reaction time) may be readily ascertained by those having ordinary
skill in the substrate coating arts once apprised of the present
invention.
Although the method of the invention is disclosed above as being
carried out in a chamber of a chemical vapor deposition (CVD)
furnace, it will be understood that the etching step may be carried
out in any chamber that is sealed from the environment and into
which a flow of the gases may be introduced. An advantage of
carrying out the process in a CVD furnace is that the etching,
purging, and coating steps may be carried out sequentially in the
furnace chamber without the need to move the composite materials
from one chamber to another during the process. Thus, the method of
the invention may be programmed as a complete cycle in the CVD
furnace and accomplished in one run. This feature of the invention
provides a distinct advantage over procedures wherein a liquid
solution etchant is used to remove binder phase material because
such liquid solutions cannot be introduced into the same chamber
employed to coat the substrate by a CVD or PVD process. Also, it
has been found that the substrate may be kept cleaner and the depth
of etching may be better controlled when using a gaseous etchant as
opposed to a liquid etchant.
The step of etching binder phase from the composite material
substrate preferably should remove binder material to a depth of
about 3 to about 15 microns and more preferably about 4 to about 6
microns, into the substrate surface. Too shallow an etching depth
does not provide a significant enhancement in coating adhesion. Too
great an etching depth weakens the surface of the substrate.
Etching time may be varied to account for differences in the
susceptibility of the particular binder phase to be removed by the
etchant gases. Those having ordinary skill in the substrate coating
arts may readily determine the etching time necessary to provide a
desired depth of etching for a particular substrate. The substrate
temperature at which the etching step should be carried out to
remove the desired amount of binder material also will depend upon
the character of the binder, but may be readily determined.
Deposits of a phase of W.sub.x Co.sub.y C (wherein x=3-9 and
y=2-6), also known as .eta. (eta) phase, may form on the surface of
composite material substrates. Eta phase is a hard and brittle
carbon-deficient phase that may easily fracture and may be produced
when etching substrates that include tungsten, carbon, and cobalt.
The presence of eta phase significantly degrades the properties of
composite material substrates used in material removal (i.e.,
cutting, drilling, threading, boring, etc.) applications and,
therefore, the generation of eta phase preferably should be avoided
during the etching and coating of composite material substrates and
other substrates by appropriately adjusting the etching and coating
conditions. For example, relative to composite material substrates
including nickel binder, composite material substrates having
cobalt binder should be etched at lower substrate temperatures in
order to inhibit the formation of eta phase on the surface of the
substrate. The inventors also have determined that if hydrogen gas
is present during an etching step employing a gaseous etchant, the
hydrogen may combine with any carbon present as WC and any cobalt
within the substrate material and will thereby make the WC
deficient in carbon, resulting in formation of an eta phase. One
possible reaction representative of formation of an eta phase is as
follows:
The eta phase does not convert to CoCl.sub.2, as is required for
the precursor elements of the eta phase to leave the substrate
surface as a gas. The inventors have concluded that formation of
eta phase is significantly inhibited when using nitrogen or certain
other gases in substitution for hydrogen gas used in conjunction
with etchant gas during the etching step. A representation of a
possible reaction occurring during etching of a cobalt-containing
composite material by a hydrogen chloride etchant gas, and wherein
the etchant gas is not applied to the material in combination with
hydrogen gas, is believed to be as follows:
The CoCl.sub.2 is a gaseous product that is swept from the coating
furnace during the purging step.
Accordingly, the inventors have discovered that the step of etching
a substrate including tungsten, carbon, and a binder phase
including cobalt will not be satisfactorily accomplished if the
gaseous etchant mixture includes hydrogen gas. For example, when
etching binder phase from a composite material cutting insert
composed of tungsten carbide particles in a binder composed
predominantly of cobalt using a gaseous etchant mixture of hydrogen
chloride and hydrogen gases, cobalt residue remains in the voids
etched between the tungsten carbide particles and the undesirable
eta phase may form, significantly reducing substrate toughness. The
inventors have found that nitrogen gas may be advantageously
substituted for hydrogen gas to prevent formation of eta phase.
More broadly, to better ensure removal of etched binder material so
as to avoid formation of eta phase on substrate surfaces, gases
that may be substituted for hydrogen gas in the gaseous mixture
used in the substrate etching step include those selected from one
or more of nitrogen gas and other gases that do not react with the
substrate or removed binder and that do not change the oxidation
state of the substrate. Such other gases are believed to include,
for example, helium, argon, and neon gases.
The foregoing representations of reactions that may occur during
the etching process are provided only to better illustrate possible
reaction mechanisms, and should not be considered to in any way
limit the scope of the invention.
As discussed above, the etchant gas that may be used in the etching
step of the method of the present invention may be any gas that
will suitably remove the desired depth of binder phase in a surface
region of the composite material substrate that is being etched.
Such etchant gases include, for example, HCl gas, H.sub.2 F.sub.2
gas, and the gaseous form of any of the Group VIIA elements in the
periodic table of the elements.
The purging step occurring subsequent to the etching step is
necessary to remove any products of the etching reaction and any
etchant remaining in the chamber, and to reduce any explosion
hazard. Any gas or combination of gases that will suitably remove
the reactant products and remaining etchant gases and that will not
react with the binder or hard particle constituents of the
composite material may be used as the purging gas. Suitable purging
gases include, for example, one or more of nitrogen, helium, and
argon gases.
Once etched, the substrate may then be coated with a wear-resistant
or other coating material by any conventional composite substrate
coating process. Such processes include, for example, CVD, PVD,
plasma arc, and super lattice processes. Still other composite
material coating procedures will be readily apparent to those of
ordinary skill in the substrate coating arts. All such other
suitable coating processes may be used in the present method
subsequent to the gas etching procedure. Any coating process used
to deposit wear-resistant material on a composite material
substrate etched by the procedure of the present method is carried
out under conditions by which the wear-resistant material may at
least partially infiltrate the voids in the composite material
created by removal of the binder material. One of ordinary skill
may readily determine such conditions without undue
experimentation.
On a basic level, the present invention also is directed to a
method for removing binder material from a region of a composite
material, and the inventive method need not include the subsequent
coating step. A composite substrate having a roughened surface may
be produced by such a method. Roughened composite substrates may be
used in a variety of known applications, including, for example,
ball point pen balls, wherein a roughened surface provides enhanced
traction. Additionally, substrates may be etched by the present
method and then coated at some later time and/or at a different
facility, rather than in a single procedure in which the etching
and coating steps are combined. One example of a coating that may
be applied in a procedure removed in time from the etching
procedure and/or at another facility is a diamond coating.
Following are actual examples illustrating embodiments of the
method of the present invention. The following examples are
illustrative examples only, and should not be considered to in any
way limit the scope of the present invention.
EXAMPLE 1
A Bernex 250 CVD coating furnace was prepared by introducing into
the coating chamber of the furnace a 10 l/min (liters/minute) flow
of hydrogen gas to establish a 200 mbar hydrogen gas pressure
within the chamber. The chamber was then heated to 850.degree. C. A
cemented carbide substrate composed of H-91 grade material
available from Stellram, LaVergne, Tenn., was placed in the
prepared furnace chamber and the chamber atmosphere was heated to
850.degree.. H-91 grade material is composed of 88.5 weight percent
tungsten carbide, 11.0 weight percent cobalt, and 0.5 weight
percent of a mixture of TiC, TaC, and NbC. The material exhibits a
hardness of 89.7 HRA, 14.40 g/cc density, and a transverse rupture
strength of approximately 389,000 psi.
The flow of hydrogen gas was then stopped, and a concurrent flow of
20 l/min nitrogen gas and 1 l/min hydrogen chloride gas was
introduced into the chamber to provide a chamber pressure of 800
mbar. Binder was etched to a depth of approximately 5 microns into
the substrate's surface by the running the concurrent N.sub.2 /HCl
gas flow into the chamber for 25 minutes, and then discontinuing
the flow of HCl gas. While maintaining the chamber atmosphere at
850.degree. C., the chamber was then purged for 15 minutes by
continuing the 20 l/min flow of N.sub.2 gas while establishing a 60
mbar chamber pressure.
After purging the chamber, and without removing the etched
substrate from the chamber, the etched substrate was coated with a
moderate temperature milling and turning coating (referred to
herein as "MT-milling coating"), which is a multi-layer insert
coating consisting of two TiN layers of approximately 1 micron with
a TiCN layer of approximately 3 microns disposed between the two
TiN layers. The MT-milling coating was deposited on the substrate
by introducing into the furnace chamber flows of gases that will
produce coatings of TiN, TiCN, and then TiN, in that order, as
follows.
Before the coating procedure began, the chamber atmosphere was
heated to 920.degree. C. and the chamber pressure was reset to 160
mbar. After that pressure was established, a first TiN layer was
provided on the substrate by initiating a 9 l/min nitrogen gas
flow, increasing the hydrogen gas flow to 14 l/min, and initiating
a 2.1 ml/min flow of TiCl.sub.4 gas. The concurrent flows of the
three gases were allowed to proceed for 60 minutes while the
chamber pressure was maintained at approximately 160 millibars.
During the 60-minute period, the furnace temperature was lowered
5-10.degree. C. every fifteen minutes so as to be at approximately
895.degree. C. at the end of the period.
The interposed TiCN coating was produced by lowering the nitrogen
gas flow to 8 l/min, and then resetting chamber pressure to 60
mbar. The TiCl.sub.4 gas flow was then raised to 2.4 ml/min. Once
all flows were constant, a flow of CH.sub.3 CN gas generated by
vaporizing a 0.3-0.4 mL/min flow of liquid CH.sub.3 CN flow was
initiated. The concurrent gas flows were continued for 2 hours,
during the first hour of which the furnace temperature was reduced
to 870.degree. C. At the end of the 2-hour period, the flows of
CH.sub.3 CN and TiCl.sub.4 gases were discontinued.
To prepare for deposition of the second TiN layer, the flow of
nitrogen gas was discontinued, chamber pressure was set to 500
mbar, hydrogen gas flow was reset to 12 l/min, and furnace
temperature was set at 940.degree. C. When that temperature was
reached, the pressure was set to 60 mbar, hydrogen gas flow was
reset to 10.5 l/min, nitrogen gas flow was reset to 4.5 l/min, and
TiCl.sub.4 gas flow was reset to 1.4 l/min. On reaching the target
1.4 l/min TiCl.sub.4 gas flow rate, the flows were continued at
temperature for 30 minutes, at which time the pressure was reset to
800 mbar and the gas flows were continued for an additional 30
minutes. The furnace was then purged by shutting off the TiCl.sub.4
gas flow, resetting chamber pressure to 600 mbar, raising hydrogen
gas flow to 12 l/min, and lowering nitrogen gas flow to 3.5 l/min.
The reset gas flows were continued for fifteen minutes. The furnace
was then subjected to a cool down procedure.
It was observed that the MT-milling coating infiltrated at least a
portion of the voids etched in the substrate's surface.
EXAMPLE 2
The Bernex 250 CVD furnace used in Example 1 was prepared using the
procedure described in that example. A cermet substrate composed of
SD-5 material, but having the same size and shape as the substrate
in Example 1, was placed into the coating furnace and the furnace
atmosphere was heated to 920.degree. C. SD-5 material is a cermet
grade material available from Stellram, LaVergne, Tenn., and is
composed of TiCN and Mo.sub.2 C particles in a Co/Ni binder. SD-5
material has the approximate elemental composition 45.2 Ti, 22.6
Mo, 10.9 C, 2.3 N, 19.0 Ni, and exhibits the following approximate
mechanical properties: 91.8 HRA hardness, 6.30 g/cc density, and a
transverse rupture strength of 300,000 psi. After heating the
furnace atmosphere to 920.degree. C., the Co/Ni binder was then
etched to a depth of 5 microns from the substrate's surface using
concurrent flows of hydrogen chloride and nitrogen gases at the
flow rates, pressure, and reaction time used in Example 1 above.
The furnace chamber was then purged using a 20 l/min flow of
N.sub.2 gas for 15 minutes at a chamber pressure of 60 millibars.
The etched composite was then coated with an MT-milling coating
using the procedure of Example 1. The MT-milling coating
infiltrated the etched voids to a depth of 5 microns .+-.
approximately 1 micron, and with approximately 1 micron of the
coating disposed above the substrate's surface.
EXAMPLE 3
Three Stellram cutting inserts of type SEKN-42-AF4B composed of
SD-5 material (as described in Example 2) were first etched and
then coated with the MT-milling coating by the following
procedure.
A CVD furnace chamber was prepared using the procedure described in
Example 1. The SD-5 cutting inserts were then inserted into the
furnace chamber and were etched using the procedure of Example 2.
Once etched, the inserts were coated with MT-milling coating by the
procedure of Example 1. The MT-milling coating produced on the
etched inserts by the foregoing procedure was approximately 5
microns in thickness and the surface TiN layer infiltrated the
voids etched in the inserts' surfaces. Approximately 5 microns of
the coating extended above the inserts' surfaces. FIG. 1 is a
photomicrograph (2040.times.) of a prepared cross-section through
the surface of one of the etched and coated SD-5 inserts. The
photomicrograph shows the infiltration of the MT-milling coating
into the voids etched in the insert surface. The infiltration of
the coating into the voids increased the adherence of the coating
to the insert and improved the thermal shock resistance of the
coating.
The three etched and coated SD-5 inserts and three inserts of the
same type that were unetched and uncoated were inserted at one time
into a six-insert Teledyne (Lavergne, Tenn.) HSM-3E4-45 EZ shear
cutter that was then installed on a 2 H.P. Bridgeport milling
machine and tested under the following milling conditions:
8620 steel at 20-25 RockwellC hardness
800 surface feet per minute
0.050 inch depth of cut
0.004-0.005 inches per tooth (feed rate)
16.5 inch length of cut
2.5 inch width of cut
The SD-5 inserts were pulled and inspected after every two 16.5
inch milling passes. After the initial two passes, one uncoated
SD-5 insert had one thermal crack started and the five remaining
SD-5 inserts did not exhibit thermal cracks. After ten passes, all
three unetched/uncoated SD-5 inserts exhibited one or more thermal
cracks while only one etched and coated SD-5 insert exhibited a
single thermal crack. Milling testing was concluded after 18
passes, at which point each unetched/uncoated insert exhibited 2-4
thermal cracks on their used edges, while only one thermal crack
existed in one etched and coated insert. The conditions of an edge
surface of each of the three etched/coated SD-5 inserts after 10
and 18 passes are shown in FIGS. 2a-c and 3a-c, respectively. The
used edge conditions of the three unetched/uncoated SD-5 inserts
after 10 and 18 passes are shown in FIGS. 4a-c and 5a-c,
respectively.
EXAMPLE 4
Three Stellram SEKN-42-AF4B cutting inserts composed of T-14
material were etched and then coated with an MT-milling coating by
the method used in Example 3. T-14 material is a milling grade
material available from Stellram (LaVergne, Tenn.) having a nominal
composition composed of 70 weight percent tungsten carbide and 20
weight percent of a combination of tantalum carbide, niobium, and
titanium carbide. Particles of the foregoing material are bound
together by a cobalt binder that is 10 weight percent of the total
weight of the material. T-14 material typically exhibits a hardness
of 91.20 HRA, 12.43 g/cc density, and an average transverse rupture
strength of 296,000 psi.
The three etched and coated T-14 inserts and three unetched and
uncoated T-14 inserts of the same type were inserted at one time
into a six-insert HSM-3E4-45 EZ shear cutter, installed on a 2H.P.
Bridgeport milling machine, and tested under the following milling
conditions:
4140 steel at 40-45 Rockwell C hardness
500 surface feet per minute
0.050 inch depth of cut
0.004-0.005 inch per tooth (feed rate)
14 inch length of cut
2.5 inch width of cut
After four passes under the above conditions, the depth-of-cut
regions of the etched and coated T-14 inserts showed no evidence of
thermal cracking or deformation as examined under a 40.times.
microscope. After four passes all unetched and uncoated T-14
inserts exhibited numerous thermal cracks with one insert at the
thermal crack breakout stage. As used herein, "thermal crack
breakout" is the point at which two or more thermal cracks connect
and just before the insert surface fractures. Photomicrographs
showing the condition of the depth-of-cut region of the three
etched and coated T-14 inserts and the three unetched and uncoated
T-14 inserts are shown in FIGS. 6a-c and 7a-c, respectively. The
test demonstrated that using the present invention's method to etch
composite substrates with cobalt binder to a 10 micron depth and
then coating the substrates provides for a coated insert showing
significant edge strength and enhanced resistance to coating/edge
delamination, coating spalling, and edge fracture. Results similar
to the SD-5 insert milling tests of Example 3 were achieved in that
the T-14 substrates etched and coated by the present invention's
method provide an increased resistance to thermal cracking of the
cobalt-based material.
EXAMPLE 5
Stellram SEKN-42-AF4B type cutting inserts composed of H-91 grade
material were obtained. Half of the H-91 inserts were coated with
MT-mill coating in a Bernex 325 furnace using an automated
procedure substantially similar to the above-described MT-milling
coating procedure so as to provide a layered coating on the inserts
composed of approximately 1 micron TiN, approximately 3 microns
TiCN, and then 1 micron TiN, all such thicknesses being
approximate. The remaining H-91 grade inserts were etched in a
Bernex 250 CVD furnace using the procedure of Example 1 and the
etched inserts were then MT-milling coated in the furnace by the
procedure described in Example 3. Actual total MT-milling coating
thicknesses were determined to be 6.2 microns for the
unetched/coated inserts and 5.4 microns for the etched/coated
inserts. A photomicrograph of the coated surface of one of the
etched and coated H-91 inserts is shown in FIG. 8. The figure
demonstrates the infiltration of the coating into the etched
inserts' surfaces.
Single etched/coated or unetched/coated H-91 inserts were installed
on a seven-insert Teledyne HSM-5E4-45 5-inch diameter EZ shear
cutter, installed on a 25 H.P. Kearney-Trecker milling machine, and
tested under the following milling conditions:
ASTM A536 (F-33100 unified UNS) nodular cast iron
875 surface feet per minute
0.125 inch depth of cut
0.008 feet per tooth
20 inch length of cut
4 inch width of cut
Each insert was pulled after one pass and examined. After one pass,
each of the tested unetched/coated inserts exhibited 6-7 thermal
cracks, while the tested inserts that had been etched and coated by
the method of the present invention exhibited only a single thermal
crack. 30.times. photomicrographs of an etched/coated H-91 insert
after one milling pass and an unetched/coated insert after one
milling pass are provided as FIGS. 9 and 10, respectively.
This example 5 compared inserts composed of identical base
materials and identical coatings, with the only significant
difference being that the test samples of one set were first etched
by the present method and the MT-milling coating had infiltrated
the resulting interstices in the inserts' surfaces. The etched and
infiltrated inserts exhibited significantly increased resistance to
thermal cracking relative to the unetched coated inserts.
EXAMPLE 6
A heavy metal part containing 90 weight percent tungsten metal
particles suspended in 10 weight percent of an iron/nickel binder
was etched and coated with an MT-milling coating using the
procedures of the invention as generally described in the foregoing
examples involving insert composed of SD-5 material. 21.times.
photomicrographs of sections of the etched and coated metal part
taken through the coated surface are shown in FIGS. 11a-11d. The
photomicrographs shown the infiltration of the coating into the
voids etched in the metal part's iron-nickel binder.
In each of the foregoing Examples 1-5, all composite material
substrates that were etched using the method of the present
invention failed to show evidence of the formation of an eta
phase.
Those of ordinary skill in the substrate coating and treatment arts
will appreciate that various modifications and changes in the
details of the invention that has been disclosed herein may be made
without detracting from the advantages provided by the invention,
and it will be understood that all such changes and modifications
remain within the principle and scope of the invention as expressed
in the appended claims.
* * * * *